Bacterial conjugation can promote genetic exchange between biological kingdoms and is largely responsible for the evolution of antibiotic resistances among eubacteria. Genetic exchange between bacteria, and between bacteria and their hosts, promotes pathogenesis, such as Agrobacterium tumefaciens induced tumorigenesis in plants. Even when transferred genes are not inherited, the transfer of DNA and protein between cells may have a heritable effect. Transferred molecules of DNA can serve as templates for the repair of damaged DNA in the recipient, and transferred proteins may alter and existing epigenetic state. Such exchanges are important, therefore, for two reasons: assessing the extent and impact of genetic exchange in pathogenesis and determining the potential for altering a cellular program through the exchange of non- genetic material. I have been studying the molecular factors which accompany transfer of genetic material during conjugation. These factors are particularly intriguing because they are required primarily or specifically in the recipient organism, may be encoded by the donor cell chromosome rather than the virulence factors, and are required in a species-specific manner. I have found that the conjugal transfer of one co-factor, the RecA protein of Escherichia coli, can trigger the release of a latent phage. The transfer of a chromosomal protein can therefore affect a heritable state of both cell and phage and may have implications for the development of a disease susceptibility in humans.